Drawn strand filled tubing wire

ABSTRACT

A wire for use in medical applications. The wire is formed by forming a bundle from a plurality of metallic strands and positioning the bundle within an outer tube. The tube and strands are then drawn down to a predetermined diameter to form a wire for use in medical devices. The wire may be covered with an insulating material.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/203,986, filed Aug. 15, 2005, now U.S. Pat. No. 7,501,579, which is acontinuation-in-part of U.S. patent application Ser. No. 10/524,387,filed Oct. 3, 2005, now U.S. Pat. No. 7,420,124, which is related to andclaims the benefit under 35 U.S.C. 119 and 35 U.S.C. 365 ofInternational Application PCT/U52004/029957, filed Sep. 13, 2004, nowPublication No. WO 05/081681, which is a non-provisional application ofU.S. provisional application Ser. No. 60/543,740, filed Feb. 11, 2004.The disclosures of each of the foregoing references are explicitlyincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drawn strand filled tubing wire foruse in medical applications and in particular to such wire where thereis a need to apply an electrical voltage to human tissue.

2. Description of the Related Art

Implantable devices used in the medical field for applying electricalvoltage are customarily meant to stay implanted for several years. Suchdevices are used as pacing leads, for example. These medical devicesmust possess several characteristics including electrical conductivity,corrosion resistance, and biocompatibility. The medical devicesgenerally need to be flexible for snaking through arteries, for example.

Drawn filled tubing wire is a type of wire that has been usedextensively in medical devices. This wire includes an outer shell thatis filled with an electrically conductive material. While the materialsused for the outer shell are strong, they tend to be susceptible tocorrosion when contacted by body tissues and fluids. Therefore, drawnfilled tubing wire for medical use is customarily coated with aninsulating material such as silicone to prevent contact with human bodytissue. Pacing leads for applying an electric potential to the heartusually comprise two or three drawn filled tubing wires. Such leads aredescribed in U.S. Pat. Nos. 5,716,391, 5,755,760, 5,796,044, and5,871,531. A portion of the wires in such leads is generally encasedwithin a biocompatible material such as platinum, tantalum filledplatinum, tantalum filled platinum-iridium, or the like to allow anelectrical voltage to be applied from the wire to the desired tissuearea. A problem with such biocompatible materials is that they haveinsufficient strength and have limited electrical conductivity, andtherefore must be combined with the wire.

Referring to FIGS. 1A and 1B, a prior art pacing lead is shown for usein medical applications. Implantable cardio defibrillator (ICD) 20 isused for sensing electrical activity in the heart and for delivering ashock if heart activity slows or stops. ICD 20 is implantable and hasflexible, elongated conductive lead 26 (FIG. 1B) with electricalconnector 22 extending from one end thereof to plug into control 24 forcontrolling ICD 20 and for providing the electrical supply. Control 24is implanted just beneath the skin, often in the chest or abdomen.

Lead 26 is constructed from two or three electrically conductive wires27 such as wires having an alloy exterior tube filled with highlyconductive silver, for example. Each wire 27 is substantially coveredwith insulating material 29. Lead 26 is then substantially covered withinsulating material 28. At two locations along lead 26, coils 30 arelocated which are made from a biocompatible material such as platinum,tantalum filled platinum, tantalum filled platinum-iridium, or the like.Coils 30 are secured to individual wires 27 of lead 26 by any suitableprocess including laser welding. The portion of wire 27 in contact withcoil 30 has insulating material 29 removed to allow for the weldingprocess. These coils 30 form the contacts which engage the heart tissueat specific locations to deliver an electrical voltage, when control 24senses the need to deliver such voltage.

The interface between insulating material 28 and coils 30 must behermetically sealed to prevent fluids from contacting wires 27 of lead26 and causing corrosion and possible eventual failure of the ICD.Problems exist in that the achieving a hermetic seal of a polymericmaterial and a metal is difficult and costly. The bond may besusceptible to corrosion and bodily fluid leaking into the area betweencoil 30 or insulating materials 28, and wires 27 of lead 26. Inaddition, the materials used to form coils 30 are very flexible and maybe easily damaged simply from handling the coils. The welding processbetween wires 27 of lead 26 and coils 30 is a further step in themanufacturing process which increases the cost of production of ICD 20.

In the medical device industry, leads are used to transmit an electricalvoltage from an electrical supply source to an area in a human body. Thelead interfaces with tissues in the body so that an electrical signalmay be introduced to a particular area of the body. Such leads may beimplanted in a patient at any location in the body where theelectrophysiology needs to be monitored and/or artificially altered.Specific applications may be implantable defibrillators or pacing leads.The leads may also be used for pain relief or pain suppression in theback or spine relating to diseases such as Parkinson's disease. The leadmay be further implanted in the stomach to subside hunger pains. Forpatients with neurological damage, the leads might be used to replacethe nerve and act to transmit electrical signals from one place toanother in the body. These devices are most certainly used in humanshowever, they are not limited to humans and may be adapted for use inanimals.

The devices are designed for long term implantation and must haveseveral properties including resistivity, corrosion resistance,radiopacity, reliability, stiffness, fatigue life, weldability, MRIcompatibility, and biocompatibility. Other characteristics of the deviceinclude a predetermined ultimate tensile strength, Young's modulus,level of inclusions, fracture toughness, and percent elongation. Inaddition, the types of materials used, the construction, and the cost ofmanufacturing the device are all factors.

It is therefore an object of the present invention to provide a pacinglead with improved wires which eliminate the need for conductive coils.

It is therefore a further object of the present invention to reduce therisk of corrosion of the pacing lead.

It is therefore another object of the present invention to improveconductivity and flexibility of the pacing lead.

SUMMARY OF THE INVENTION

The present invention provides a wire for use in accomplishing theobjects set out hereinabove. The wire includes a plurality of strands,wires, or elements of material which are arranged in a particularorientation and are twisted or braided into a bundle before beingpositioned within an outer tube. The strands are formed from any of aplurality of materials to define the mechanical and electricalcharacteristics of the device. Such characteristics include corrosionresistance, strength, electrical conductivity, radiopacity, reliability,stiffness, fatigue life, weldability, MRI compatibility,biocompatibility and the like. In addition, a hollow strand may be usedto allow for fluid transfer along the length of the device for use indrug delivery to the patient, for example. Alternatively, a fiber opticstrand could be included as well as electrically insulated strands. Thetubing and strands are then drawn to a predetermined diameter to form awire for use in medical devices. The wire may be covered with aninsulating material.

An advantage of the present invention is that by use of the presentinvention, the need for conductive coils in pacing leads is eliminated.

Another advantage of the present invention is that the risk forcorrosion of the wires used in pacing leads and the like issignificantly reduced.

Yet another advantage of the present invention is that by using a wirehaving a plurality of strands or elements within the outer tubing, thewire is more flexible and is less subject to mechanical failure due tofatigue than prior art wires.

Still another advantage is a wire with improved conductivity and lowerbattery consumption when used in pacing leads.

Yet still another advantage is a wire which is more comfortable to thepatient.

A yet further advantage is that the wire would be more reliable as, evenif one strand were to fail, there are numerous strands within the wirewhich would not fail, i.e., the strands have redundancy.

A yet another advantage of the wire is that it would provide designflexibility.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features and objects of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1A is a perspective view of a prior art implantable cardiodefibrillator using materials in accordance with the prior art.

FIG. 1B is a sectional view of FIG. 1A taken along line 1B-1B.

FIG. 2A is a perspective view of an implantable cardio defibrillatorusing a lead in accordance with the present invention.

FIG. 2B is a sectional view of FIG. 2A taken along line 2B-2B.

FIG. 3 is an exploded perspective view of a plurality of twisted strandsassembled within a tube.

FIG. 4 is a sectional view of the assembled plurality of twisted strandsand outer tube of FIG. 3.

FIG. 5 is a sectional view of the assembled plurality of strands andouter tubing of FIG. 4 after drawing of the assembly.

FIG. 6 is a sectional view of the assembled plurality of strands andouter tubing after drawing of the assembly to a smaller diameter thanthat shown in FIG. 5.

FIG. 7 is a sectional view of the assembled plurality of strands andouter tubing after drawing of the assembly to a smaller diameter thanthat shown in FIG. 6.

FIG. 8 is a sectional view of an alternative arrangement of a pluralityof strands.

FIG. 9 is a sectional view of the alternative arrangement of FIG. 8located in an outer tubing.

FIG. 10 is a sectional view of a third arrangement of a plurality ofstrands assembled with an outer tubing.

FIG. 11 is a sectional view of a fourth arrangement showing theplurality of strands assembled with an outer tubing FIG. 9 locatedwithin a second outer tubing.

FIG. 12 is a sectional view of a fifth arrangement showing a tubecontaining a plurality of strands which surround a core.

FIG. 13 is a sectional view of a sixth arrangement showing a tubecontaining a core which is contained in a second tube and which is inturn surrounded by strands and filled tubes.

FIG. 14 is a sectional view of a seventh arrangement showing a tubecontaining a core surrounded by a tube and a plurality of strands.

FIG. 15 is a cross sectional view of the structure of the seventharrangement of FIG. 14 taken along the lengthwise direction of the wire.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the exemplification set outherein illustrates the invention, the embodiments disclosed below arenot intended to be exhaustive or to be construed as limiting the scopeof the invention to the precise forms disclosed.

DESCRIPTION OF THE PRESENT INVENTION

Referring to FIG. 2A, one example of a device utilizing the lead formedin accordance with the present invention is illustrated. Implantablecardio defibrillator (ICD) 32 includes an elongated lead used to shockthe heart when the heart rate becomes irregular. ICD 32 has first end 34and second end 36. First end 34 is provided with electrical connectors38 which engage control 40 which includes an electrical supply orbattery pack. Control 40 is implanted just beneath the skin of thepatient and is designed to have a long life so that frequent removal andreplacement is unnecessary. Second end 36 is mounted in the area of thebody being sensed which, in this example, is the heart. Second end 36 isprovided with barbs 42 which anchor the end of ICD 32 in place. Lead 43extends the length of ICD 32 and includes three wires 44. End 46 of onewire 44 has barbs 42 mounted thereon and is exposed. Wire end 46 acts asa sensor to monitor the heart's activity and initiate shock treatmentsto the heart when necessary.

Referring to FIGS. 2A and 2B, lead 43 is covered with a layer ofinsulating material 48 which may be formed from any suitable,biocompatible material such as, for example, urethane, to electricallyinsulate the conductor. Insulating material 48 substantially extends thelength of lead 43 with the exception of wire end 46 and contact sections50A and 50B. One wire 44 of lead 43 is exposed to the body tissues atend 46 and at each contact sections 50A and 50B so as to interface withthe body tissues and deliver an electrical shock as necessary. By usingthree wires to define three electrical contact points along lead 43,electrical potential is created between end 46, and contact sections 50Aand 50B. Contact sections 50A and 50B are spaced apart a predetermineddistance which coincides with the anatomy of the particular patient.

Referring now to FIGS. 3 and 4, wire 44 is constructed such that it actsas both the electrical contact surface and the electrical lead, thusmaking coils 30 of FIG. 1A unnecessary for providing the interfacebetween the conductor and the body tissue. Thus, corrosion at theurethane to metal joint of FIG. 1B between insulating material 28 andcoils 30 is eliminated. In addition, since fragile coils 30 are alsoeliminated, the cost of assembly and materials is reduced.

Wire 44 comprises drawn strand filled tubing wire formed from outertubing 52 and a plurality of strands, elements or wires 54. Each of thestrands may comprise a drawn filled tube wire. The initial size of thestrand diameter may be in the range of 1 mm-11 mm. The plurality ofstrands 54 are twisted or braided into a braided bundle as shown in FIG.3 with the outer strands being rotated about center strand 56. Thetwisted plurality of strands 54 is positioned within outer tubing 52 andthe conductor is thereafter drawn to the desired diameter. The twistingof strands 54 into a braided bundle ensures that wire 44 has the correctorientation of strands 54 throughout its length after being drawn. Aswire 44 is drawn, strands 54 are lengthened and align in thepredetermined arrangement. The diameter of drawn outer tubing 52 may bein the range of 2-12 mm, for example, but may be smaller for certainapplications.

There are several advantages to using strands 54 inside tubing 52.Strands 54 provide a more flexible wire 44 which is an important factorwhen snaking wire 44 through the patient's arteries, for example. Themore strands 54 used, the greater the flexibility. Additionally, overallfatigue life is improved for wire 44. For example, if one strand 54 hasa crack initiated at a high stress point or stress riser so strand 54ultimately fails, fatigue must be reinitiated in another of strands 54until all of strands 54 fail before wire 44 fails completely, thusimproving the life of wire 44.

Wire 44 is a metal-to-metal composite that combines the desired physicaland mechanical properties of two or more materials into a single lead.Wire 44 is drawn at ambient temperature. However, as the drawing processoccurs, the temperature and pressures increase significantly causing theformation of mechanical bonds between strands 54 and outer tubing 52. Byusing the drawn strand filled tube technology, dissimilar materials maybe combined to provide a variety of properties in a single conductor 54.The composite then has an outer tubing layer 52 which is biocompatibleand electrically conductive while the core material is designed toprovide strength, conductivity, radiopacity, resiliency, MRIenhancement, or the like.

In the embodiments shown in the figures, wire 44 is provided with 19strands 54. The number of strands 54 however may be any desired numberto fill tubing 52, or to provide particular properties to wire 44 aswill be discussed further hereinbelow. The diameter of the individualstrands 54 also determines the number of strands used to fill outertubing 52. In addition, the number of strands 54 directly relates to thecost of wire 44.

Outer tubing 52 is constructed from a biocompatible material so that thenecessary electrical contact is made directly between wire 44 and bodytissues. Such materials may include platinum or platinum alloys,tantalum or tantalum alloys, tantalum filled platinum, tantalum filledplatinum-iridium, or the like. Outer tubing 52 has a thickness which isdependent upon the type of wire 44 which is desired. The thicker thewall of outer tubing 52, the more rigidity it provides to wire 44. Ifthe wall of outer tubing 52 is made thinner, wire 44 is more flexibleand the cost of materials is reduced. The outer tubing however, shouldnot be made too thin so as to risk compromising the outer wall of wire44.

Referring to FIG. 4, a first embodiment of wire 44 is illustrated havingidentical strands 54. In this instance, strands 54 comprise drawn filledtubing wires. Strand 54 is a metal to metal composite comprising anouter tubing 58 formed from any suitable material possessing thecharacteristics desired in wire 44. One such material may be acobalt-nickel-chromium alloy known as ASTM Standard F562. The ASTM F562material has characteristics including strength and long fatigue life.The strands 54 are filled with silver 60 because silver is ductile andmalleable, and has very high electrical and thermal conductivity. Oneacceptable type of strand is filled with 41 percent silver by weight.However, any suitable amount of silver or other suitable conductor maybe used. For example, if 60 percent silver, by weight, is used in thestrands, the strands have higher electrical and thermal conductivity.However, less ASTM F562 is then used and the strength of the strand isreduced. The combination of metals is ultimately determined by thedesired properties for each strand 64. An alternative material which maybe used in place of ASTM F562 material is a similar alloy. In additionto ASTM F562 materials such as ASTM Standard F90, F538, and othernickel, cobalt based super alloys, titanium, nitinol such as ASTM F2063,and tantalum materials may be used. A material which has a much longerfatigue life than ASTM F562 and which is described in U.S. patentapplication, entitled “Cobalt Nickel Chromium Molybdenum Alloy With AReduced Level Of Titanium Nitride Inclusions,” filed Sep. 5, 2003, thedisclosure of which is hereby incorporated herein by reference, may alsobe useful in particular applications of lead 44.

Once the strands 54 are positioned within outer tubing 52, wire 44 isdrawn to reduce the diameter to the desired size. Referring to FIGS. 5,6, and 7, wire 44 is illustrated in stages as it is drawn to a smalldiameter. As the conductor is drawn, the strands 54 impinge upon oneanother and inner surface 62 of outer tubing 52. The round shape of eachstrand 54 is compromised by being compressed into adjacent strands 54and inner tubing surface 62. The material used for outer tubing 52 isrelatively ductile compared to ASTM F562, for example, which is whyinner tubing surface 62 becomes deformed as outer tubing 52 iscompressed against strands 54. The thickness of outer tubing 52 furtherdepends upon the ability of the tubing material to apply forces againststrands 54 to compress and deform the strands without compromising theouter tubing.

Referring to FIG. 7, center strand 56 has a substantially hexagonalcross section while the rest of strands 54 have non-hexagonal crosssections because they are in the transition area between the core andinner tubing surface 62. If the number of strands 54 is increased, thelayers of strands surrounding center stand 56 would increasingly show asubstantially hexagonal cross section, the hexagonal shape migratingfrom center strand 56 toward the outer transition layers.

In order to eliminate some of the deformation of inner tubing surface62, outer strands 54 could be swaged to develop facets which wouldengage surface 62. The interface between strands 54 and inner tubingsurface 62 may then be preserved due to the more uniform pressure beingexerted between strands 54 and outer tubing 52. This may help to reducethe risk of compromising a thinner walled outer tubing 52.

After wire 44 has been drawn to an appropriate length or cut from a rollof drawn strand filled tubing wire, for example, insulating material 49(FIG. 2B) is applied to the outer surface of outer tubing 52. Insulatingmaterial 49 is applied to each wire 44 in any suitable manner toelectrically insulate wires 44 and define the three contact points withthe body, sensor 46 and both contact sections 50A and 50B. Referring toFIG. 2B, a portion of insulating material 49 is removed from wire 44′ todefine contact section 50A with the other two wires 44″ and 44′″remaining completely insulated at contact section 50A. Similarly, aportion of insulting material 49 is removed from wire 44″ to definecontact section 50B. Insulating material 49 is removed at contact end 46of wire 44′″ to provide a sensor. The thickness of insulating material49 can be reduced since the sealing engagement between insulatingmaterial 28 and coils 30 of the prior art is eliminated. This sealingengagement is provided to prevent fluids from coming into contact withconductor 20 of the prior art. By completely encasing the inner,electrically conductive portion or strands 54 with a biocompatible outertubing 52, the risk of contact of fluids with strands 54 issubstantially eliminated. Thinner coatings of insulating material 49makes wires 44 and thus lead 43 more pliable, allowing for easierinsertion into a patient.

In addition, the manufacturing of wire 44 may be simplified by theelimination of coils 30. Insulating material 49 is simply removed fromwire 44 at sensor 46 and contact sections 50A and 50B to expose wire 44.Alternatively, sleeves of insulting material 49 may be positioned aboutthe outer surface of outer tubing 52 and drawn down with wire 44.

When constructing lead 43, insulating material 48 is then applied to thebundle of three wires 44′, 44″, and 44′″, by any suitable method so asto insulate and contain wires 44 while exposing the electrical contactareas sensor 46, and contact sections 50A and 50B. Insulating material48 also maintain the orientation of the wires, keeping the exposedportions of wires 44 aligned with the openings defining contact sections50A and 50B in insulating material 48.

Strands 54 located in outer tubing 52 may include various types ofmaterials to provide specific mechanical attributes to wire 44.Referring to the embodiment shown in FIGS. 8 and 9, several of strands54 are strands 64 as in the previous embodiment. The inner silver 60 ofstrands 64 provides electrical conductivity through wire 44 while outertubing 58 adds strength. To further strengthen wire 44 and improvefatigue life, solid strands 66 of materials including ASTM F562, and thelike may be included in the plurality of strands 54. Other propertiesmay be specifically addressed in wire 44 by adding different types ofstrands 54. For example, by adding solid platinum or tantalum strands68, radiopacity of wire 44 is enhanced. Tungsten has excellent corrosionresistance and may be added to improve that particular property of wire44. Ultimately, any types of strands 54 may be combined to create a lead44 have predetermined properties.

An alternative method of building the stiffness of wire 44 as shown inFIG. 11 would be to position strands 54 within a first tube of amaterial such as ASTM F562, for example, and then to position the ASTMF562 or strand filled tube wire in second, outer tubing 72 having theproperties required of outer tubing 52. Second tubing 72 would be of amaterial such as platinum, tantalum filled platinum, tantalum filledplatinum-iridium, or the like, all of which are biocompatible andelectrically conductive. The entire assembly could then be drawn to thedesired diameter. Further, second outer tubing 72 could be in the formof a strip which is wrapped around first tube 52 and laser welded.

Referring to FIG. 10, a further embodiment is illustrated in which oneof strands 54 is a tubular, hollow strand 70. Hollow strand 70 wouldallow for passage of fluid through wire 44 which may be useful forapplications involving drug delivery, for example.

Further, FIG. 11 also shows a DFT strand 64 which includes a silver core64, tubing 58, and an insulation layer 76. Additionally, FIG. 11 shows astrand 64 with a glass, fiber optic, core 78 and a metallic tubing 58.If desired, the tubing 58 could be deleted from core 78.

Referring to FIG. 12, a further embodiment is illustrated having anouter shell or tube 82 composed of a platinum alloy containing 10%iridium. Inside tube 82 is a central core 86 formed of tantalum RO5200elements or strands of material surrounded by strands 84 of 35NLTmaterial. The wire product is manufactured by first forming the strandedtantalum bundle 86, then surrounding the tantalum elements or strandswith strands 84 of 35NLT and then inserting the composite bundle ofstrands into a tube 82 and drawing down the tube 82 and its contents toform the product as shown in FIG. 12. It should be noted that no voidsare present within the tubular structure, the tantalum strands orfilaments 86 are tightly packed together. Furthermore, the 35NLT strandsor elements 84 are tightly packed together.

It should be noted that in this description the words strand andfilament are used interchangeably.

FIG. 13 shows a still further embodiment wherein an outer shell 90 iscomposed of a platinum alloy containing 10% iridium. The core of thisstructure is composed of a 41% silver material 92 enclosed within a35NLT tube 94. Tube 94 and silver material 92 may comprise a drawnfilled tube (DFM™). Surrounding tube 94 are six silver strands orfilaments 96 which are wrapped around tube 94. Surrounding silverstrands 96 are twelve filaments or strands consisting of alternatingtantalum RO5200 strands 102 and drawn filled tubes 98 composed of 35NLTtubes 98 filled with a metal material containing 41% silver 100. Theentire structure is manufactured by first forming a composite strandedor braided cable composed of elements 92, 94, 96, 98, 100, and 102,enclosing the stranded cable within tube 90, and thereafter drawing downthe tube 90 and the enclosed cable to form the structure shown in FIG.13. Note again that no voids are present within the structure.

FIG. 14 shows a still further embodiment. The outside shell or tube 106is composed of a platinum alloy containing 10% iridium material. Withinthe tube is a drawn filled tube core formed from a shell 110 of a 35NLTmaterial which is filled with a 41% silver material 108. Surroundingshell 110 are six tantalum RO5200 strands or filaments 112. Elements108, 110, and 112 are first formed as a cable which is then placedinside shell 106. The entire composite structure is then drawn down toform the structure shown in FIG. 14.

FIG. 15 shows a longitudinal section through the wire of FIG. 14. It canbe clearly seen in FIG. 15 that tantalum filaments 110 are woundhelically around tube 110 as gaps 114 are shown between the varioustantalum strands 112.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles.

1. A metallic wire, comprising: an outer cylindrical shell of a firstbiocompatible metal; and a plurality of wire elements disposed withinsaid shell, at least one of said wire elements including an outer tubingof a second biocompatible metal filled with a core of a thirdbiocompatible metal, said outer shell and said plurality of wireelements compacted together such that substantially no voids existwithin said outer shell.
 2. The wire of claim 1, wherein said firstbiocompatible metal comprises platinum or a platinum alloy, said secondbiocompatible metal comprises an alloy of cobalt, nickel, chromium, andmolybdenum, and said third biocompatible metal comprises silver or asilver alloy.
 3. The wire of claim 1, wherein said plurality of wireelements are stranded together by twisting.
 4. The wire of claim 1,wherein said plurality of wire elements include at least one solid corewire element made of a fourth biocompatible metal and not including saidouter tubing.
 5. The wire of claim 1, wherein said plurality of wireelements includes at least one hollow tube.
 6. The wire of claim 1,including an additional outer cylindrical shell covering said outershell, said additional outer cylindrical shell made of a fourth metal.7. The wire of claim 1, including a layer of electrically insulatingmaterial at least partially covering said outer shell.
 8. A metallicwire, comprising: an outer cylindrical shell of a first biocompatiblemetal; a core element of a second biocompatible metal within said outershell; and a plurality of wire elements disposed between said coreelement and said outer shell, said plurality of wire elements togetherforming a substantially continuous annular layer between said coreelement and said outer shell in cross section, said wire elementscompacted between said core element and said outer shell such thatsubstantially no voids exist within said outer shell.
 9. The wire ofclaim 8, further comprising an interior wire element disposed withinsaid core element.
 10. A metallic wire, comprising: an outer cylindricalshell of a first biocompatible metal; a core element of a secondbiocompatible metal within said outer shell; and a plurality of wireelements disposed between said core element and said outer shell, saidplurality of wire elements together forming a substantially continuousannular layer between said core element and said outer shell in crosssection, said wire elements compacted between said core element and saidouter shell such that substantially no voids exist within said outershell, wherein said wire elements each include an outer tubing of athird biocompatible metal with said outer tubing filled with a core of afourth biocompatible metal.
 11. A metallic wire, comprising: an outercylindrical shell of a first biocompatible metal; a core element of asecond biocompatible metal within said outer shell; and a plurality ofwire elements disposed between said core element and said outer shell,said plurality of wire elements together forming a substantiallycontinuous annular layer between said core element and said outer shellin cross section, said wire elements compacted between said core elementand said outer shell such that substantially no voids exist within saidouter shell, wherein said wire elements include: a plurality of firstwire elements each including an outer tubing of a third biocompatiblemetal with said outer tubing filled with a core of a fourthbiocompatible metal; and a plurality of second wire elements eachincluding a solid core wire element of a fifth biocompatible metal andnot including said outer tubing.
 12. A method of making a metallic wire,said method comprising the steps of: providing an outer cylindricalshell of a first biocompatible metal, the shell having a first outerdiameter; inserting a plurality of wire elements into the outer shell toform a wire construct, at least one of the wire elements including anouter tubing of a second biocompatible metal with the outer tubingfilled with a core of a third biocompatible metal; and drawing the wireconstruct to form a drawn wire of reduced diameter with the outer shellhaving a second outer diameter less than the first outer diameter, andthe plurality of wire elements being compacted together such thatsubstantially no voids exist within the outer shell.
 13. The method ofclaim 12, further comprising, prior to said inserting step, theadditional steps of: forming the plurality of wire elements into abundle; and twisting the bundle of wire elements to form a twistedstrand.
 14. The method of claim 12, further comprising, prior to saidinserting step, the additional step of: twisting the wire elements abouta core element wherein, in said inserting step, the core element and thewire elements are both inserted into the outer shell.
 15. The method ofclaim 14, further comprising, prior to said drawing step, the additionalstep of inserting at least one interior wire element within the coreelement.
 16. The method of claim 12, further comprising, after saiddrawing step, the additional step of: coating the drawn wire with anelectrically non-conductive insulating material.
 17. The method of claim12, further comprising, prior to said drawing step, the additional stepsof: providing a second outer cylindrical shell of a fourth metal; andinserting the wire construct into the second outer cylindrical shell.